The archive bit is used to determine what files have been backed up up previously on a Windows filesystem.
The bit is set if a file is modified.
A backup program can then clear the bit when it does a full backup. This allows the backup program to do an incremental or differential backup that only backs up the changes to the filesystem since the last time the bit was cleared.
Note that on programs like BrightStor ARCserve backup, you have a choice on full backups about whether or not to clear the archive bit. If you choose not to clear the archive bit, this is the same as a “copy” backup, where the backup does not affect the state of your scheduled backups.
For instance, say you did a full backup over the weekend, and differential backups during the week. If you decide you want to upgrade a server and want to do a full backup, you could run a full backup on a separate set of tapes without changing the ever-growing nightly differential set of backups by choosing not to clear the archive bit.
This would be particularly useful if you were not the one managing the regular backup process. If you don’t do this, then the following day, when the differential runs (or incremental), you would need to have the second full backup you made to get a complete restore.
The ext2 filesystem on GNU/Linux does not have an archive bit, but it does have three different time stamps (creation, modification, and access) that can be used to work around this. The problem, though, is you need an extra process to make decisions on this.
Samba works around this by tweaking the owner bits on ext2. For an explanation on how this is done, and some further explanation of Windows filesystem bits, see this document. To determine what files have the archive bit set on a Windows (or DOS) filesystem, use:
Backups either locally or over the network, which we’re seeing more of lately can all be monitored to ensure that everything is running perfectly and finishing on time. Network monitoring systems, including Solarwinds NPM and PRTG, can monitor backup programs as well to ensure they are finishing in a timely manner.